Iowa DNR
ADBNet

Water Quality Assessments

Impaired Waters List

North Raccoon River IA 04-RAC-1132

from confluence with Indian Cr. (S24 T87N R36W Sac Co.) to confluence with Cedar Cr. in S25 T88N R36W Sac Co.

Assessment Cycle
2018
Release Status
Final
Data Collection Period
Overall IR Category
4 - Water is impaired or threatened and a TMDL has been completed or is not needed.
Trend
Unknown
Created
5/29/2019 10:51:26 AM
Updated
8/1/2019 1:53:35 PM
Assessment conducted in accordance with Iowa's 2018 IR methodology
Use Support
Class A1
Partially Supported
Bacteria: Indicator Bacteria- E. coli
Support Level
Partially Supported
Impairment Code
4a - Pollutant-caused impairment. TMDL has been completed.
Cause Magnitude
Slight
Status
Continuing
Source
Unknown: Source Unknown
Source Confidence
N/A
Cycle Added
2008
Impairment Rationale
Geometric mean criterion exceeded
Data Source
Ambient monitoring: Iowa DNR-rivers
Class BWW1
WINOFI
Biological: low aquatic macroinvertebrate IBI
Support Level
Water in Need of Further Investigation (WINOFI)
Impairment Code
3b-u - Use potentially biologically impaired based on uncalibrated IBI metrics.
Cause Magnitude
Moderate
Status
Continuing
Source
Unknown: Source Unknown
Source Confidence
Low
Cycle Added
2002
Impairment Rationale
Low Biotic Index
Data Source
Biological monitoring: Iowa DNR WQMA
Class HH
Not Assessed
General Use
Not Assessed
Impairment Delistings
No delistings for this assessment cycle.
Documentation
Assessment Summary

The Class A1 (primary contact recreation) uses are assessed as "not supported" due to levels of indicator bacteria (E. coli) that slightly violate state water quality standards. The Class B(WW1) aquatic life uses remain assessed as "partially supporting" based on results of DNR/SHL biological sampling in 2012, 2013 and 2015, 2016. The fish consumption uses remain not assessed. The sources of data for this assessment include (1) the results from the DNR/SHL ambient monthly monitoring station downstream from Sac City in Sac County (STORET station 10810001 (formerly station 423014)) located approximately 5 miles south of Sac City from 2014-2016, (2) results of USGS ambient monitoring near Sac City at station 05482300 from August 2012 through August 2013, and (3) results of DNR/SHL biological sampling conducted in 2012, 2013 and 2015, 2016.

Assessment Explanation

[Note 1: This assessment of the Class A1 (primary contact recreation) uses and the water quality data are used, in part, for the adjacent downstream segment (IA 04-RAC-1131).]

[Note 2: A TMDL for pathogen indicator (E. coli) impairments in the Raccoon River basin was prepared by DNR and approved by EPA in June 2008. Because this TMDL covers the primary Section 303(d) impairment identified for the 2006 assessment/listing cycle, this waterbody was moved from IR Category 5a from the 2006 assessment/listing cycle to IR Category 4a (impaired; TMDL approved) for the 2008 cycle. This waterbody remains in IR Category 4a for the current cycle.]

The Class A1 (primary contact recreation) uses are assessed (monitored) as "partially supported" based on levels of indicator bacteria that exceeded state water quality criteria. The geometric means of indicator bacteria (E. coli) in the 24 samples collected during the recreational seasons of 2014 through 2016 at DNR station 10810001 near (downstream from) Sac City were as follows: the 2014 geometric mean was 292 orgs/100 ml, the 2015 geometric mean was 256 orgs/100 ml, and the 2016 geometric mean was 632 orgs/100 ml. All three recreation season geometric means exceeded the Class A1 geometric mean criterion of 126 orgs/100 ml. Twelve of the combined 24 samples (50%) exceeded Iowa’s Class A1 single-sample maximum criterion of 235 orgs/100 ml. According to U.S. EPA guidelines for Section 305(b) reporting and DNR’s assessment/listing methodology, if the geometric mean is greater than 126 orgs/100 ml., the primary contact recreation uses should be assessed as "impaired" (see pgs 3-33 to 3-35 of U.S. EPA 1997b). Thus, because at least one recreation season geometric mean exceeded criteria for Class A1 uses, these uses are assessed as "partially supported."

The Class B(WW1) aquatic life uses are assessed (evaluated) as “partially supporting” based on biological data collected in 2012, 2013 and 2015, 2016 by the DNR/SHL stream biological monitoring project. A series of biological metrics which reflect stream water quality and habitat integrity were calculated from the biocriteria sampling data. The biological metrics are based on the numbers and types of benthic macroinvertebrate taxa and fish species that were collected in the stream sampling reach. The biological metrics were combined to make a fish community index of biotic integrity (FIBI) and a benthic macroinvertebrate index (BMIBI). The indexes rank the biological integrity of a stream sampling reach on a rising scale from 0 (minimum) to 100 (maximum). The 2012, 2013 and 2015, 2016 BMIBI scores were 29 (poor), 47 (fair) and 63, 69 (both good) No FIBI/fish community samples were collected in this segment in the previous five years. The aquatic life use support was assessed (evaluated) as partially supporting (=PS), based on a comparison of the BMIBI scores with biological impairment criteria (BIC) established from a statistical analysis of data collected at stream ecoregion reference sites from 1994-2008. The BMIBI BIC is 62. This segment passed the BMIBI BIC 2/4 times (2015, 2016) in the last five years (2012-2016). This assessment is considered evaluated because the drainage area (709 mi2) above this sampling site was greater than the maximum limit (500 mi2) that was used to calibrate the Iowa wadeable stream impairment criteria. Even though this site failed the BMIBI BIC, it is uncertain as to whether or not this segment is meeting the aquatic life criteria because the site used for the assessment doesn’t fall in the calibrated watershed size. The results of this sampling thus do not meet DNR guidelines for developing a “monitored” assessment of support of the aquatic life uses that is appropriate to support the addition of this waterbody to Iowa's Section 303(d) list. The assessment type for these waters will be considered "evaluated" (indicating an assessment with relatively lower confidence) as opposed to “monitored" (indicating an assessment with relatively high confidence). Such waters will be placed in either Category 2b or 3b of the IR and thus will be added to the state’s list of “waters in need of further investigation.”

Results of chemical/physical water quality monitoring at DNR station 10810001 near (downstream from) Sac City, however, suggest “full support” of the aquatic life uses. Monitoring showedno violations of Class B(WW1) water quality criteria for 35 Ammonia samples (maximum = 0.8 mg/L), 36 Dissolved Oxygen samples (minimum = 5.9 mg/L), 36 Temperature samples (maximum = 25.3° c), 36 Chloride samples (maximum = 93 mg/L), or 36 Sulfate samples (maximum = 220 mg/L) occurred during monitoring from January 2014 to December 2016.1 of the 35 samples (3%) analyzed for pH (range = 7.3 to 9.1) violated the Class B(WW1) criteria during the 2014-2016 monitoring period. According to U.S. EPA guidelines (U.S. EPA 1997b, page 3-17) and Iowa DNR's assessment/listing methodology, a violation frequency of significantly greater than 10% for conventional parameters such as pH suggests impairment of aquatic life uses. Because the frequency of violations for this parameter is not greater than 10 percent, these results do not suggest impairment of the Class B(WW1) aquatic life uses.


Monitoring and Methods
Assessment Key Dates
9/10/2012 Biological Monitoring
8/12/2013 Biological Monitoring
7/27/2015 Biological Monitoring
1/13/2014 Fixed Monitoring Start Date
12/8/2016 Fixed Monitoring End Date
8/11/2016 Biological Monitoring
Methods
230 Fixed station physical/chemical (conventional plus toxic pollutants)
315 Regional reference site approach
320 Benthic macroinvertebrate surveys
380 Quantitative physical habitat assessment
420 Indicator bacteria monitoring